Evidence for multiple superconducting gaps in the filled skutterudite compound LaRu4As12

Abstract

Superconducting properties of the filled skutterudite compound LaRu${}_{4}$As${}_{12}$ were investigated both as a function of temperature and magnetic field. At $T\ensuremath{\ll}{T}_{\mathrm{c}}=10.45$ K, the electronic contribution to the specific heat was found to be at variance with the predictions for an $s$-wave superconductor with one energy gap. In constant applied fields up to ${H}_{\mathrm{c}2}(0)\ensuremath{\approx}10.2$ T, multiple gaps have been further inferred from both a nonlinear magnetic-field dependence of the specific heat in the zero-temperature limit and a positive curvature of the upper critical field in the vicinity of ${T}_{\mathrm{c}}$. Thus, LaRu${}_{4}$As${}_{12}$ appears to be a rare multiple-gap superconductor with cubic symmetry. Intriguing evidence for multiband effects is observed in the compound with enhanced superconducting properties as compared to other skutterudite superconductors.